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Interesting concept Antonov, thanks for the link.

I can see the benefit of increased top speeds over aircraft like the Osprey but would n't there be alot of inertia to overcome to retract the blades once they are spinning at full speed? I wonder what mechanism they'd use in that slim disc?

Hmm......hmmm.gif

:woot.gif:

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Interesting concept Antonov, thanks for the link.

I can see the benefit of increased top speeds over aircraft like the Osprey but would n't there be alot of inertia to overcome to retract the blades once they are spinning at full speed? I wonder what mechanism they'd use in that slim disc?

Hmm......hmmm.gif

:jaw-dropping:

Basically a similar setup to that a radial engine uses for its connecting rod to the pistons. A shaft turns, a quarter turn pulling the lever ends to pull the blades inside.

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The biggest challenge I can see in such a design is coming up with a rotor that is rigid enough for helicopter use and still be flexible enough to be retracted into the housing. Granted I am sure the aviation firms have a few tricks up their sleeves, but this is an interesting concept. At least the vehicle they illustrated has a wing to potentially allow it to land conventionally, should there be a rotor failure. I've always wondered what would happen to an Osprey if it took some sort of damage that would prevent the rotors to tilt from horizontal flight to vertical as the blades are so big that a belly landing with the blades attached would be impossible.

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As always - weight and CoG will be the main challenges. A big 'what if' would be upon getting back to landing configuration, what if one of the blades does not deploy.... ugh

Have you ever heard the Mitch Hedberg joke "Escalators cannot break - they can only become stairs"? Well, if a blade breaks, then this thing becomes an airplane.

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Have you ever heard the Mitch Hedberg joke "Escalators cannot break - they can only become stairs"? Well, if a blade breaks, then this thing becomes an airplane.

The tricky bit though is there had better be safeguards in place to catch the rotor head to keep it from spinning up with only three blades extended, or the vibration could rip the rotor head apart. Then it won't be an airplane, just a crash waiting to happen.

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Have you ever heard the Mitch Hedberg joke "Escalators cannot break - they can only become stairs"? Well, if a blade breaks, then this thing becomes an airplane.

Have you ever heard of centrifugal force? Well, if the disk is turning while the aircraft is in flight and one of the blades does not deploy, then this thing becomes a spinning mess and a hole in the ground.

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Have you ever heard of centrifugal force? Well, if the disk is turning while the aircraft is in flight and one of the blades does not deploy, then this thing becomes a spinning mess and a hole in the ground.

Why wouldn't one blade deploy? This would obviously have a gearing mechanism where all the blades are connected to an interconnected series of arms where one motor moves the whole arm assembly and all the blades move out or in. That kind of design would be very simple and reliable in the extreme. Even in the unlikely event of something going wrong with a blade (like getting hit with ground fire), all you need to do is retract the system. You don't even need the pilot to do it - it is trivial to have the computer perform a retract if it detects undue vibration.

What happens to an airplane if a wing falls off? What happens to a helicopter if a blade falls off? Are those actually concerns?. This thing has two independent mechanisms for generating lift - if it flies it's going to be the safest thing up there, not the least.

Edited by spejic
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Basically a similar setup to that a radial engine uses for its connecting rod to the pistons. A shaft turns, a quarter turn pulling the lever ends to pull the blades inside.

The problem with that is that if the blades are still turning, they'll turn faster if you retract them - conservation of angular momentum and all that. The trick is to stop them first, which implies a braking mechanism and raises the problem that killed the X-rotor. One of the stopped blades must end up facing the wrong way, making the whole thing asymmetric and hugely increasing the control problems. The only way round that that they could think of was a symmetrically-profiled rotor blade, which causes its own set of problems.

Still, if DARPA has working models (and that's not just CGI), it must be possible in principle. I wonder how many prototypes they've built, and how many are still working?

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Think the main engineering issue will be in the design of the bearing assemblies used to guide the blades while they retract or extend. You will certainly have varing loads on the blades based on their position. Since they will structurally be overhung beams you will need to acount for the moment (torque) at the bearings (support points.) Going to be interesting with the loads from: lift, air vehicle forward or rearward acceleration, and any G's that it may be pulling. Sounds like a nice three dimensional problem.

Mark S.

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what are they using to counter torque in hover?

I'd guess asymmetric thrust from those two big turbofans.

From my point of view, that thing makes the V-22 look positively simple...not that it can't be done, but it'd be EXPENSIVE...just like any other innovative new technology.

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I've always wondered what would happen to an Osprey if it took some sort of damage that would prevent the rotors to tilt from horizontal flight to vertical as the blades are so big that a belly landing with the blades attached would be impossible.

In that scenario, they'd probably sacrifice the blades to save the rest of the plane. Put the gear down, and land it like a normal airplane. The blades will shred and throw the pieces all over creation, but the pieces will for the most part be thrown away from the aircraft because of the direction the blades rotate (in toward the fuselage from the bottom).

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what are they using to counter torque in hover?

I'm glad someone said it. That was my first thought. My next thought was how the heck are they going to put the mechanical linkages to retract spinning blades into that disk?

Guys, helicopters are inherently evil creatures to begin with. They LIKE to break and do it often. This is an interesting innovation, but with all of the other rotorcraft technology that is coming out now, this just seems like a baaaaad idea.

Jon

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